Spectral analysis of stress wave propagation through inflated lungs

Spectral and coherence analyses of signal pairs were used to evaluate transit time at different frequencies. The results of the spectral method indicated that the stress wave propagation in inflated lungs occurred at relatively low frequencies (20-120 Hz) and long wavelengths (1-8 cm). Wave velocity varied with frequency. Shear or Rayleigh wave velocities were detected in the low-frequency range (35-60 Hz). Longitudinal waves of higher velocities were detected only at isolated higher frequencies above 80 Hz. The spectral method can detect a wave velocity in situations where the frequency content of the signal masks the peaks in the cross correlation function. The spectral method is particularly useful for detecting the transit time for a single-velocity wave of a combination of waves having velocities associated with different frequency bands. Spectral analysis of stress wave propagation in lungs resulted in information that was not obtained by cross correlation analysis. Spectral analysis provided further evidence for the presence of stress waves propagated through lung parenchyma